Commissioning and performance of the GE1/1 slice test detectors

The performance of the CMS muon system, as it was instrumented in Run 1, will be deeply called into questions in the next few years. The foreseen increase in luminosity of LHC, up to 5 times the nominal value, will induce a huge increase of the pileup and of the radiation background. The CMS Collaboration then started an overall upgrade program, which foresees interventions on both the already existing chambers and electronics, but also the completion of the existing muon stations with new detectors in the high-eta region.The first of these new stations, called GE1/1, is expected to reduce the Level-1 muon trigger rate and improve the tracking performance in a harsh radiation environment. The technology selected is the Gas Electron Multiplier (GEM), in particular Triple-GEM, whose complete qualification, performed in the last few years of R and D, led to the approval of the installation of the full station in the second Long Shutdown. A first installation of a demonstrator started at the beginning of 2017 five Triple-GEM superchambers were installed in the CMS muon system with the aim of gaining operational experience and demonstrating the integration of the GE1/1 system into the trigger.This contribution will present the results obtained from the commissioning of the installed chambers. The performance of the detectors in the 2017 and beginning of 2018 LHC Run will be discussed too.